Clinical courses of 4 patients who developed aggressive B-cell lymphomas during JAK1/2 inhibition. Timelines (A-D). Frequencies of immunoglobulin rearrangement in the bone marrow during myelofibrosis and lymphoma development in conventionally treated patients (N = 44) compared with patients treated with JAK1/2 inhibitor (N = 54) (E). NHL, non-Hodgkin lymphoma; CR, complete remission; CRu, complete remission unconfirmed; rNHL, remission of NHL; sAML, secondary acute myeloid leukemia.